Difluoroacetic acid is used as an intermediate in the pharmaceutical and agrochemical industry. Different ways of preparing difluoroacetic acid or its salts have been disclosed.
For instance it is known to prepare difluoroacetic acid by chlorine-fluorine exchange. JP 06-228043 (ASAHI GLASS CO LTD) 16 Aug. 1994 discloses a reaction of dichloroacetyl chloride with a secondary amine followed by treatment of the N,N-disubstituted dichloroacetamide product with a fluorinating agent, e.g. KF, to give N,N-disubstituted difluoroacetamide. The amide product is hydrolyzed to give difluoroacetic acid.
Preparation of difluoroacetic acid from tetrafluoroethylene has been reported for instance in U.S. Pat. No. 2,442,995 (DU PONT DE NEMOURS & CO.) Aug. 6, 1948 which discloses a process whereby tetrafluoroethylene is reacted with ammonia to yield 2,4,6-tris(difluoromethyl)-s-triazine which is then hydrolyzed in the presence of NaOH to yield difluoroacetic acid.
JP 07-242587 (ASAHI GLASS CO LTD) 19 Sep. 1994 discloses the preparation of difluoroacetic acid by a two-step process wherein tetrafluoroethylene is reacted with a primary or secondary amine in the presence of water and, optionally, a tertiary amine to obtain a difluoroacetamide of formula CHF2CONR1R2 which is then hydrolyzed to difluoroacetic acid in the presence of concentrated acids or alkalis.
JP 2008-162902 (CENTRAL GLASS CO LTD) 17 Jul. 2008 discloses the preparation of a difluoroacetic acid metal salt by reaction of a 1-alkoxy 1,1,2,2-tetrafluoroethane (R1O—CF2CF2H), e.g. 1-methoxy-1,1,2,2-tetrafluoroethane, with a metal hydroxyde or a metal alkoxide; the 1-alkoxy 1,1,2,2-tetrafluoroethane R1O—CF2CF2H having been prepared by reaction of tetrafluoroethylene with the corresponding alcohol R1OH in the presence of a base.
These processes have the drawback that complex intermediates (e.g. triazine, amides, alkoxyethanes) have to be prepared and isolated before hydrolysis can be carried out. Additionally, hydrolysis of the intermediate is typically not quantitative and the by-products of the process cannot be easily disposed of or recycled into the process.